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Re: [libvirt] Per-guest configurable user/group for QEMU processes



On Mon, 27 Feb 2012 12:48:55 -0300
Marcelo Cerri <mhcerri linux vnet ibm com> wrote:

Just one more point. I'd like to validate the direction that I'm
getting. 

I updated the XML parse and replaced the "seclabel" member in
virDomainDef with:

    size_t nseclabels;
    virSecurityLabelDefPtr *seclabels;

I also added a "model" field in virSecurityLabelDef to identify the sec
driver. So, my idea is to replace any access to the seclabel  with a
search by the model name. So, for example, instead of using

	secdef = def->seclabels;

I'll use:

	secdef = virDomainDefGetSecurityLabelDef(def,
			SECURITY_SELINUX_NAME);

virDomainDefGetSecurityLabelDef will search for a seclabel with the
given model/name.

I'm having to update too many parts in the code and I'd like
to save some time if this is not the right direction.

Regards,
Marcelo


> Great. I think it is a good approach. The lack of an enclosing tag
> still bothers me. But, as you said, there's no serious problem not
> having it and I can live with that :)
> 
> I believe the primary driver should be defined in qemu.conf, so I
> would like to replace the "security_driver" config with two new
> configs: primary_security_driver and additional_security_drivers. The
> last one would contain a list of security divers separated by commas,
> for example:
> 
>    primary_security_driver = "apparmor"
>    additional_security_divers = "dac,another_driver"
> 
> For device seclabel's, I intend to add a "model" attribute to specify 
> which security driver is being overriding (if it's not given, the 
> primary driver is considered).
> 
> <domain ...>
>    ...
>    <devices>
>      <disk type='file' device='disk'>
>        <source file='/path/to/image1'>
>          <seclabel relabel='no' model='dac'/>
>        </source>
>        ...
>      </disk>
>      <disk type='file' device='disk'>
>        <source file='/path/to/image2'>
>          <seclabel relabel='yes' model="selinux">
>            <label>
>              system_u:object_r:shared_content_t:s0
>            </label>
>          </seclabel>
>        </source>
>        ...
>      </disk>
>      ...
>    </devices>
>    <seclabel type='dynamic' model='selinux'>
>      <baselabel>text</baselabel>
>    </seclabel>
>    <seclabel type='static' model='dac'>
>      <label>501:501</label>
>      <imagelabel>501:501</imagelabel>
>    </seclabel>
> </domain>
> 
> What do you think?
> 
> Regards,
> Marcelo
> 
> On 02/23/2012 07:34 PM, Daniel P. Berrange wrote:
> > On Thu, Feb 23, 2012 at 06:38:45PM -0200, Marcelo Cerri wrote:
> >> On 02/23/2012 05:47 PM, Daniel P. Berrange wrote:
> >>> On Thu, Feb 23, 2012 at 05:41:27PM -0200, Marcelo Cerri wrote:
> >>>> Hi,
> >>>>
> >>>> I'm starting working on an improvement for libvirt to be able to
> >>>> support per-guest configurable user and group IDs for QEMU
> >>>> processes. Currently, libvirt uses a configurable pair of user
> >>>> and group, which is defined in qemu.conf, for all qemu processes
> >>>> when running in privileged mode.
> >>>>
> >>>> This topic was already commented in qemu mailing list
> >>>> (http://lists.nongnu.org/archive/html/qemu-devel/2011-10/msg00758.html)
> >>>> but, as this requires changes in libvirt API, I'd like to
> >>>> discuss what would be the best solution for it.
> >>>>
> >>>> A solution (as proposed in the link above) would be to extend the
> >>>> security driver model to allow multiple drivers. In this case, an
> >>>> example of the XML definition would be:
> >>>>
> >>>>    ...
> >>>> <seclabel type='dynamic' model='selinux'>
> >>>> <label>system_u:system_r:svirt_t:s0:c633,c712</label>
> >>>> <imagelabel>system_u:object_r:svirt_image_t:s0:c633,c712</imagelabel>
> >>>> </seclabel>
> >>>> <seclabel type='dynamic' model='dac'>
> >>>> <label>102:102</label>
> >>>> <imagelabel>102:102</imagelabel>
> >>>> </seclabel>
> >>>>    ...
> >>>>
> >>>> I don't know if this is a clean solution because the usual option
> >>>> would be to enclose the block above in a "<seclabels>" tag. But
> >>>> as this would break the actual API, it's not viable.
> >>>
> >>> While it is true that we would ordinarily have an enclosing tag
> >>> like<seclabels>, there's no serious problem not having it. Just
> >>> having two (or more)<seclabel>   elements in a row is just fine,
> >>> given our backwards compatibility requirements.
> >>>
> >>> So I think this option is just fine.
> >>
> >> I agree that this is a good solution, considering the XML
> >> compatibility. But, what about virDomainGetSecurityLabel? It could
> >> access the first security label or ignore the DAC driver (and maybe
> >> another function could be added to access the whole list of
> >> seclabels), but it doesn't seem to be the best solution.
> >
> > We can just keep virDomainGetSecurityLabel()/virNodeGetSecurityModel
> > as only ever handling the primary security driver.
> >
> > Then add some new APIs which are more general
> >
> >    int virNodeGetSecurityModelCount(virConnectPtr conn);
> >    int virNodeGetSecurityModelList(virConnectPtr conn,
> >                                    virSecurityModelPtr models,
> >                                    int nmodels);
> >    int virDomainGetSecurityLabelList(virDomainptr dom,
> >                                      virSecuriyLabelptr labels,
> >                                      int nlabels);
> >
> >
> > Regards,
> > Daniel
> 
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